The present invention relates generally to vehicles and, more particularly, to sound attenuating materials utilized within vehicles.
It is generally considered desirable to reduce the level of noise within a vehicle passenger compartment. External noises, such as road noise, wind noise, engine noise, vibrations, etc., as well as noises emanating from within passenger compartments, may be attenuated through the use of various acoustical materials. For example, sound attenuating materials are conventionally provided in conjunction with carpeting for floor panels, upholstery for door panels and headliners, etc.
The attenuation of external noise is conventionally referred to as sound transmission loss (STL). The attenuation of internal noise is conventionally referred to as sound absorption. The acoustic impedance of a material is defined as material density times acoustic velocity, and is expressed in units of Rayls (Newton-seconds/meter3). Acoustic impedance measures material resistance to air moving through the material as a function of frequency. (In contrast, static air flow resistance Rayl measurements are independent of frequency.) Thus, for fibrous materials, acoustic impedance depends upon the density of the fibrous material, fiber diameter, thickness and related parameters. Generally, the greater the blanket density and the finer the fibers, the higher the acoustic impedance. Moreover, thicker increase acoustic impedance. The ability of a material to attenuate noise is conventionally defined by the material""s STL, acoustic impedance, and absorption characteristics.
Various sound attenuating materials have been developed for use in reducing noise levels within passenger compartments of vehicles. For example, U.S. Pat. No. 4,851,283 to Holtrop et al., proposes a thermoformable laminate for use in headliners. The headliner comprises a non-woven fabric bonded to a foamed polymer sheet. The fabric is formed from a blend of low melting staple fibers and high melting staple fibers.
U.S. Pat. No. 5,298,694 to Thompson proposes a non-woven acoustical insulation web. The web comprises thermoplastic fibers, and particularly a blend of melt-blown microfibers and crimped bulking fibers.
U.S. Pat. No. 5,677,027 to Masuda et al., proposes a sound insulating structure comprising a covering layer, a panel, and a cushioning layer. The cushioning layer comprises a first fiber such as polyethylene terephthalate (PET) and a second fiber that is of a shell-core construction wherein the majority of the core is PET.
U.S. Pat. No. 5,817,408 to Orimo et al., proposes a sound insulating structure which includes low and high density thermoplastic fibers. PET is preferred as a thermoplastic synthetic fiber.
U.S. Pat. No. 4,529,639 to Peoples, Jr. et al. proposes a molded foam-backed carpet assembly which includes a carpet layer, a moldable thermoplastic polymer layer and one or more foam pads fusibly bonded to the thermoplastic layer and extending over less than the entire surface of the thermoplastic polymer layer to provide desired cushioning and sound and thermal insulation only in preselected areas of the carpet.
In general, the ability of conventional materials to attenuate sound increases as the amount of material increases. Unfortunately, increasing the amount of material often increases the weight of sound attenuating material, which may be undesirable. Accordingly, there is a continuing need for acoustical insulation materials for use within vehicles that exhibit superior sound attenuating properties, while also being lightweight and low in cost.
In view of the above discussion, sound attenuating composite articles for use within vehicles as floor coverings and other interior trim components are provided. According to embodiments of the present invention, a sound attenuating composite article includes first, second, and third layers of material and a porous upholstery material (e.g., carpeting) sandwiched together. The composite article is configured to have an acoustic impedance of between 4,700-6,300 Rayls in the frequency range of 100-400 Hz; an acoustic impedance of between 1,300-2,400 Rayls in the frequency range of 500-2,000 Hz; and an acoustic impedance of between 950-1,600 Rayls in the frequency range of 2,500-5,000 Hz. The composite article is also configured to have a sound absorption factor of between 0.13-0.18 in the frequency range of 100-400 Hz; a sound absorption factor of between 0.55-0.69 in the frequency range of 500-2,000 Hz; and a sound absorption factor of between 0.69-0.87 in the frequency range of 2,500-5,000 Hz. In addition, the composite article is configured to have a sound transmission loss of between 7.3-14.0 decibels (dB) in the frequency range of 100-400 Hz; a sound transmission loss of between 6.6-11.9 dB in the frequency range of 500-2,000 Hz; and sound transmission loss of between 8.0-15.0 dB in the frequency range of 2,500-5,000 Hz.
The first layer of material is a damping layer that has a thickness of less than or equal to about five millimeters (5 mm) and is configured to be attached to a surface of a panel of a vehicle (e.g., a sheet metal or polymeric component of a vehicle, such as a floor panel, door panel, etc.) in face-to-face contacting relationship therewith. The second layer of material is a decoupler layer that is attached to a surface of the first layer of material in face-to-face contacting relationship. The second layer of material has a thickness of less than or equal to about seventy millimeters (70 mm). The third layer of material is a scrim/web material that is attached to a surface of the second layer of material in face-to-face contacting relationship. The third layer of material has a thickness of less than or equal to about two millimeters (2 mm). The porous upholstery material (e.g., carpeting) is attached to a surface of the third layer of material in face-to-face contacting relationship therewith.
According to embodiments of the present invention, the damping layer is formed from bituminous material such as asphalt or asphalt modified with resins and/or polymers. The decoupler layer comprises an acoustic fiber batting and/or an acoustic foam material. The third layer of material is a scrim/web material. An exemplary scrim material is a blend of polyester and polyolefin fibers, preferably a blend of about 70% polyester fibers and about 10% polyolefin fibers.
Methods of producing sound attenuating composite articles for use within vehicles are also provided. According to embodiments of the present invention a damping layer having a thickness of less than or equal to about 5 mm is provided. Typical range of composite loss factor for the damping layer is between about 0.01 and 0.06 (as measured by the oberst method between xe2x88x9230xc2x0 C. and 70xc2x0 C.). A decoupler layer having a thickness of less than or equal to about 70 mm is provided that has an acoustic impedance of at least 5,300 Rayls, 1,160 Rayls, and 190 Rayls in the respective frequency ranges of 100-400 Hz, 500-2,000 Hz, and 2,500-5,000 Hz; has a sound absorption factor of at least 0.01, 0.27, and 0.72 in the respective frequency ranges of 100-400 Hz, 500-2,000 Hz, and 2,500-5,000 Hz; and has a sound transmission loss of at least 1.3 dB, 1.8 dB, and 2.8 dB in the respective frequency ranges of 100-400 Hz, 500-2,000 Hz, and 2,500-5,000 Hz. The decoupler layer is attached to a surface of the damping layer of material in face-to-face contacting relationship therewith.
A third layer of material having a thickness of less than or equal to about 2 mm is attached to a surface of the decoupler layer in face-to-face contacting relationship therewith. The third layer of material is a scrim/web material having a woven, non-woven, or melt blown construction which could be composed entirely of (or a blend of) nylon, polyester and polyolefin fibers. The third layer of material may be adhesively attached to the decoupler layer, or may be attached via mechanical fasteners or via other attachment means know to those skilled in the art.
The third layer of material has an acoustic impedance of at least 41,000 Rayls, 7,000 Rayls, and 1,900 Rayls in the respective frequency ranges of 100-400 Hz, 500-2,000 Hz, and 2,500-5,000 Hz; has a sound absorption factor of at least 0.00, 0.001, and 0.13 in the respective frequency ranges of 100-400 Hz, 500-2,000 Hz, and 2,500-5,000 Hz; and has a sound transmission loss of at least 1.9 dB, 1.5 dB, and 1.7 dB in the respective frequency ranges of 100-400 Hz, 500-2,000 Hz, and 2,500-5,000 Hz.
Porous upholstery material, such as carpeting, is then attached to a surface of the third layer of material in face-to-face contacting relationship therewith. In the case of carpeting, the backing side of the carpeting is attached to the surface of the second layer of material. Various additional operations may be performed on the composite article including molding operations, trim operations, etc.
Composite articles according to embodiments of the present invention can provide desired sound attenuation properties in selected vehicle locations, such as floor pans, door panels, etc. Moreover, composite articles according to embodiments of the present invention may have reduced overall weight without sacrificing sound attenuation properties.